But, how much danger does Nixon actually pose to Cuomo, who is seeking a third term as the most powerful elected official in the Empire State? To answer that, I reached out to Capital Tonight's Nick Reisman. Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Was the Cynthia Nixon candidacy expected -- by Gov. Cuomo or the political class more generally?

Reisman: I think a lot of people were surprised this became real, including Cuomo.

When Albany first heard the rumor of a Nixon candidacy, it was largely seen as being through the prism of Cuomo's problems with education advocates. Nixon has been very close with the Alliance for Quality Education, an organization that has been pushing the state to fulfill the terms of a lawsuit over equitable funding for school districts. Nixon has been to the state Capitol to advocate on this very issue.

Cuomo clearly saw this as a de Blasio-backed effort. The day after it was reported de Blasio-linked campaign consultants Bill Hyers and Rebecca Katz were working with Nixon on a potential primary, Cuomo went on a tear against the mayor. It was very Cuomoian, blasting de Blasio for being all talk and no action in TV and radio interviews that were ostensibly being held about a snowstorm. Cuomo has never faced an opponent like this in his career, so an actual strategy may take a while to emerge.

Cillizza: How much disaffection is there within the Democratic Party in the state for Cuomo? And why didn't someone more prominent -- de Blasio? -- run?

Reisman: Polling has shown Cuomo to hold steady with self-identified liberals and registered Democrats. He is, after all, the governor who successfully moved the chess pieces around, LBJ-style, to achieve the legalization of same-sex marriage.

One thing Cuomo is really good at, especially in his second term, is recalibrating. The 2014 primary he had with Zephyr Teachout was really a catalyst for the last four years in state politics and his agenda. In that primary, liberals were upset that Cuomo warred with public labor unions over pension benefits and teacher evaluations and would not ban hydrofracking.

In term two, Cuomo made peace with the state's major public employees unions and the New York State United Teachers union. He banned fracking soon after his re-election, winning him praise from environmental groups. He won the passage of an increase in the state's minimum wage, which will phase in to $15 in the New York City area in the coming years. The $15 minimum wage policy was actually on the platform of the Green Party candidate, Howie Hawkins, in 2014. The $15 minimum wage went from the Green Party to state law in two years.

But the biggest concern Democrats and liberals have with Cuomo is the state Senate, which is tied up in a major Gordian Knot. The Senate is narrowly controlled by Republicans (and it's really the last lever of power Republicans hold statewide in New York). In 2011, on the day Cuomo first took office as governor, four Senate Democrats announced they were forming their own conference, known as the Independent Democratic Conference, led by Bronx Sen. Jeff Klein. The IDC has acted as something of a coalition-style government with Senate Republicans and has grown to eight members. In the 2013-14 session, the IDC actually joined in what was known as a "majority coalition" with Republicans, sharing power in the chamber. The Republicans regained an outright majority in the Senate in 2014.

Cuomo has been seen by his liberals critics as an enabler of this arrangement: a weak Republican conference with a small advantage that he can play off the Democratic-dominated state Assembly. The IDC has gone to pains to take credit for key victories such as several increases in the minimum wage, including the $15 deal. But liberals remain dissatisfied with this arrangement, arguing that a Republican Senate has blocked reforms such as enacting early voting and strengthening abortion rights, both of which Cuomo has endorsed.

Cuomo has come under increasing pressure since Donald Trump's election to help his party gain power in the Senate. Next month is going to be really important. Last year, the New York Democratic Committee announced a unity deal between the IDC and the mainline Democrats, which was dependent upon the party winning two open seats in the Bronx and Westchester County, the latter of which the GOP hopes to be competitive in. Should both Democrats win, the theory is the party has a numerical majority.

Here's where it gets even more complicated: The Democratic world in New York will then have to convince Sen. Simcha Felder to switch conferences. Felder is a registered Democrat who sits with the Republicans in the Senate. He has also been a major thorn in the side of de Blasio. For what it is worth, Felder has said, vaguely, he will join with whichever side is "best for my constituents."

So, the math would go like this: Democrats win both seats on April 24. There would then be 32 registered Democrats to be seated in the 63-member Senate (eight IDC members, 23 mainline Democratic members and one Simcha Felder). Should Cuomo successfully claim credit for flipping the state Senate -- in the middle of the legislative session, mind you -- it could go a long way to helping stave off further liberal angst with his tenure.

As for de Blasio not running: Keep in mind being mayor of New York City is no launchpad to the Executive Mansion in Albany. Ed Koch, famously, could not do it against Mario Cuomo. Upstate Democrats would be skeptical of a de Blasio-for-governor campaign as would, quite frankly, a lot of New York City voters. A prominent person from politics running against Cuomo would face instant blow back from the institutions that are supporting the governor's re-election. Nixon is a relative outsider and, as we've seen on the national level, sometimes that doesn't hurt.

Cillizza: Break down this race. Is it Cuomo vs. Nixon? Or will there be other credible challengers? And if it's one-on-one, what does Nixon's ceiling look like?

Reisman: Currently Cuomo does have two other declared contenders in the primary aside from Nixon: Former state Sen. Terry Gipson and Randy Credico, a comedian and activist. Gipson is a one-term former lawmaker from the Poughkeepsie area who lost his re-election in 2014 and then lost an attempted comeback bid in 2016. Credico is certainly a colorful and passionate character who has played a bit role in the Wikileaks saga and has made runs for office before.

Perhaps the best, albeit imperfect, guide here is Zephyr Teachout's primary campaign in 2014. Teachout had little name recognition but harnessed a lot of the proto anti-Cuomo vibes, such as his awkwardness with the Occupy Wall Street movement and his hesitation to tax the rich, along with the anti-fracking movement and public union agita.

Teachout got 34 percent of the vote in the primary. If there's a baseline for Nixon, it's that. A Siena College poll that was taken last week, before Nixon entered the race, put her at 19 percent against Cuomo. I expect that will climb.

A lot of people expect Nixon to draw votes in New York City, given the headaches surrounding mass transit and the subway in particular. Don't be so sure. Teachout got votes in the primary from rural, upstate voters too, what I call Farmers Market Democrats. Think enclaves like Ithaca. Many of them probably voted for Bernie Sanders, are concerned with the environment and income inequality. There's not a ton of these people, but if this is close, they could be important. Meanwhile, Cuomo could still draw votes in New York City, especially from black and Latino supporters. That leaves the suburbs: the Hudson Valley and Long Island. If it's close, expect Cuomo in those areas -- a lot. Also important to note: New York's primaries are closed to people enrolled in the parties.

Cillizza: New York doesn't have term limits on its governors. But history suggests people get sick of them. Is Cuomo pushing the needle on that or no?

Reisman: Great question! We'll know in November.

But seriously, New Yorkers don't get that sick of their governors, necessarily. George Pataki served three terms. Mario Cuomo served three terms. Nelson Rockefeller left to become vice president after being elected four times. Mario Cuomo was caught up in a combination of incumbency fatigue and the 1994 Republican wave that Al D'Amato saw the chances of a little-known state senator named George Pataki being pretty good. There was fatigue with Pataki after three terms and a strong challenger in Eliot Spitzer in 2006 that hastened his retirement.

The fact remains that for governors of New York, as well as mayors of the city, the third term is always a tough one. Ask Michael Bloomberg, Ed Koch or Mario Cuomo. We haven't really gotten into the campaign season just yet with Cuomo, so we don't what his theory of the case is for why he wants to serve another four years. I think he does genuinely love being governor of New York, though. He likes that his father held that job and the prestige he sees with occupying the office.

The big "what if" remains political corruption and whether there will be any fallout from the trial of Cuomo's former close aide, Joe Percoco, who was convicted last week. There are more corruption trials to come this year, including one with developers who received major economic developments from the state in an effort to revive the Buffalo economy and just happened to donate to Cuomo's campaigns.

When he's on his game, Cuomo can be a very skilled politician governing a complicated large state with complicated politics. He sees corners and angles other people don't, can box in his opponents and has a ton of campaign cash on hand. I wouldn't be surprised if he hits $45 million or $50 million [raised] in this race.

There is generally a presumption that Cuomo is in good shape: He's got some well-connected and active labor unions on his side, like 1199 SEIU and the Hotel Trades Council. He's notched liberal victories on the minimum wage and hydrofracking and he's been increasingly blistering when it comes to Trump.